Glycoprotein nature of α2‐adrenergic receptors labeled with p‐azido[3H] clonidine in calf retina membranes

Abstract
α2,-Adrenergic receptors in calf retina membranes can be specifically labeled with the tritiated agonist p-azido[3H]clonidine. Saturation binding in the dark occurs with high affinity (1.3 ± 0.3 nM) to a single class of sites (1122 ± 67 fmol/mg protein). Irradiation of the membrane-bound radioligand results in the labeling of a peptide band with an apparent size of 65 kDa and a characteristic pharmacological profile for an α2-adrenergic receptor. The carbohydrate moieties of the α2-receptor are characterized by lectin affinity chromatography and glycosidase treatment. The Nonidet P-40-solubilized, p-azido[3H]clonidine-labeled receptors are completely retained by Con A- as well as WGA-Sepharose columns. Neuraminidase, α-mannosidase and TFMS do not affect the electrophoretic mobility of the receptor on SDS-PAGE whereas endoglycosidase F reduces the apparent size to 45 kDa.